1. Field of the Invention
This invention relates to a closure for a container which is supposed to be sold under a vacuum to protect the contents from spoiling or to assure that the contents have not been tampered with. More specifically, the invention relates to such a closure provided with a simple and foolproof means for testing that the vacuum has not been lost.
2. Discussion of the Prior Art
The prior art is, of course, replete with closures of many descriptions. However, the prior art discloses few container closures having visual and sensory and audible means for indicating the presence of a vacuum.
In the art there are one-piece metal screw-type caps with domed portions that can be pressed down by the shopper to click if there is a loss in vacuum. Also, there are two-piece caps for canning jars that include a metal lid that is drawn down under vacuum.
An indicator operable by the consumer at point of use is disclosed in Fridle et al U.S. Pat. No. 4,398,491, wherein a tape may be stripped off an aperture in the can to cause a whistling sound when air rushes in. Obviously the vacuum is spoiled when the test device is used.
A pressure indicator, as opposed to a vacuum indicator, is disclosed on the beer can structure disclosed in DiIanni U.S. Pat. No. 3,930,592, which issued Jan. 6, 1976. This patent discloses a beer can having a wall section which bows outward to show that the beer is under pressure, and when the pressure is lost, as in the opening of the can or the leaking of gas therefrom, the section snaps back to its original condition.